The court documents also reveal secret details of the anti-corruption investigation, including the arrest in March at Manchester airport of a senior Unaoil manager who was found carrying two cheques worth almost £2 million ($3.3 million)

The SFO declared it was "unpersuaded that Unaoil conducts any lawful business".

The claim will trigger panic in the boardrooms of some of the globe's best-known companies, including Rolls Royce, Halliburton, Samsung and Australia's Leighton Holdings (now called CIMIC), who paid Unaoil to help win oil, gas and other contracts from governments across the Middle East, Asia, the former Soviet states and Africa.

The ferocity of the SFO's submission also puts a spotlight on the performance Australian law enforcement agencies involved in the Unaoil probe. Despite growing evidence of serious corruption in Leighton's offshore business, implicating former senior executives Russell Waugh, David Savage and Peter Cox, Australian authorities have yet to lay a single charge.

In March, Fairfax Media exposed how Unaoil and its network of agents had paid bribes to politicians and officials to help its clients win contracts.

The revelation of the SFO's attack on Unaoil comes as the Monaco company's Australian lawyers seek to uncover the identity of the sources who helped Fairfax Media expose the international scandal.

The SFO confirmed that Unaoil's owners, the wealthy Ahsani family, "are under investigation for the payment of a series of large bribes to government officials and officers of state in a number of countries in relation to the oil and gas sector".

The size and scale of Unaoil's alleged corruption is such that the Australian Federal Police, US Department of Justice and FBI are taking charge of various aspects of the scandal. The UK government recently gave the SFO "blockbuster" funding to expand the British portion of the inquiry.

The SFO's High Court submission alleges it has "significant grounds to suspect" that Unaoil and its owners, the wealthy and well-connected Ahsani family of Monaco, "paid bribes and/or conspired together to pay bribes to high-ranking Iraqi and other public officials on behalf of" Unaoil's multinational clients.

The SFO, which is normally highly secretive about its ongoing inquiries, has been forced to reveal aspects of its operation in response to a court action lodged by the Ahsanis, listed for a hearing on December 1 in London.

Family patriarch Ata Ahsani, along with sons Cyrus and Saman, are seeking to have a judge declare that the SFO's seizure of evidence in dramatic raids in Monaco in March was unlawful. Unaoil claims the UK agency was on a "fishing expedition" that abrogated the Ahsani's rights. The Ahsanis also want the SFO to provide copies of the seized evidence.

But the SFO has described Unaoil's legal action as "hopeless" and designed to delay or compromise the ongoing criminal probe.

"The SFO has grave concerns that returning the material [seized in raids] may lead to further offending, given the nature of the material obtained by the SFO."

The SFO claims that, in contrast to statements made by Unaoil's public relations advisers, the Ahsanis are not co-operating with authorities.

In their initial interviews with the SFO in May, the three Ahsanis were questioned about corruption and "read pre-prepared statements and then gave no-comment answers." The SFO sought to interview the trio again, but "they refused."

The Serious Fraud office has also accused Unaoil of misleading the British High Court in a 2014 court case that Unaoil launched against Leighton Holdings in relation to an outstanding $25 million "marketing payment."

Leighton's offshore business was to pay Unaoil the funds to help win a $500 million Iraq government oil pipeline contract in Iraq in 2010-10. In connection to a separate pipeline contract worth $700 million, Leighton's offshore business paid Unaoil at least $75 million.

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The Australian Federal Police and SFO suspect these payments were bribes for high-ranking Iraqi politicians and officials. In the 2014 court action, Ata Ahsani denied this on oath.

Unaoil has vigorously denied corruption claims, threatening to sue Fairfax Media for $100 million for the "malicious" reporting that exposed the scandal. The company also claims that it has been extorted by an unknown third party who threatened to expose its corporate secrets.